var box=document.getElementsByClassName("box")[0];
var count=0;
box.onclick=function () {
    count++;
    if (count%2==1){
        box.style.height="200px";
        box.style.width="200px";
        box.innerHTML="大"
    }else {
        box.style.height="20px";
        box.style.width="20px";
        box.innerHTML="小"
    }
}
